1. Field of the Invention
The present invention generally relates to a peristaltic pumping apparatus and particularly, to a misloaded IV (intravenous) tube detecting circuit for a peristaltic intravenous infusion pump.
2. Description of the Prior Art
Administration of intravenous solutions to a patient is well known in the art. Typically, a solution such as saline, glucose or electrolyte in a glass or flexible container is fed to a patient's venous access site via a length of flexible plastic tubing such as polyvinyl chloride (PVC) tubing. The rate of flow of the solution is controlled by a roller clamp which is adjusted to restrict the flow lumen of the tubing until the desired flow rate is obtained.
Flow from the container to the patient may also be regulated by means other than a roller clamp. It is becoming more and more common to use an electronically controlled pump. One type of pump that is used for intravenous solution administration is a peristaltic-type pump.
Use of peristaltic pumping action is particularly well suited for the medical field. This is because peristaltic pumping action can be applied externally of the tubing carrying the intravenous solution. This maintains the sterile condition of the intravenous solution within the tubing while imparting fluid propulsion on the solution. The peristaltic pumping action can also be applied on any point on the tubing.
In a common type of peristaltic pump used in the medical field, a driving motor is connected to an array of cams which are angularly spaced from each other. The cams in turn drive cam followers which are connected to corresponding pressure fingers. These elements cooperate to impart a linear wave motion on the pressure fingers. A pressure plate is secured juxtaposed to and spaced from the pressure fingers. The pressure plate holds the tubing against the reciprocating pressure fingers to impart the wave motion on the tubing to propel the solution.
In another common type of peristaltic pump used in the medical field, a driving motor is connected via an armature to at least one roller member. The driving motor imparts a circular rotation on the armature which has adapted in the roller member. A semicircular pressure plate having the same center point as the armature is provided with the tubing located between the roller member and the pressure plate. The pressure plate holds the tubing against the roller member which imparts a circular motion on the tubing to propel the solution.
The pump also includes a door mounted on the supporting structure for movement between an open position which allows access to the pumping hardware and a closed position which impedes access to the pumping hardware.
FIG. 7 is a perspective view of a conventional peristaltic intravenous infusion pump in a state that its door is open. As shown in FIG. 7, a wall 3 of a pump body has a fluid propelling portion 2 for executing a peristaltic pumping action and grooves 4 which are respectively leading to and leading from the fluid propelling portion 2. An IV tube 1 is loaded into the groove 4 so that a portion of the IV tube 1 is located on the fluid propelling portion 2. The fluid propelling portion 2 includes pressure fingers as previously described although not illustrated in detail. The door 5 carries a pressure plate 7 associated with the pressure fingers. When the fluid propelling portion 2 is activated after the door 5 has been closed, the fluid propelling portion 2 feeds a solution in the IV tube 1 with a peristaltic pumping action by the reciprocating pressure fingers urging the tube 1 against the pressure plate 7.
Pressure sensors 6 are provided on both sides of the fluid propelling portion 2 to detect misloading of the IV tube 1. FIGS. 9A and 9B show a structure of the pressure sensor 6. Each pressure sensor 6 is comprised of a first electrode 10 provided on the front face side of the pump body, a pressure-sensitive conductive layer 11 provided on the rear face of the first electrode 10, and a second electrode 12 provided spaced from the pressure-sensitive conductive layer 11. The resistance between the first electrode 10 and the second electrode 12 is higher than a few tens M.OMEGA. when the pressure-sensitive conductive layer 11 is apart from the second electrode 12, as shown in FIG. 9A; however, when the pressure-sensitive conductive layer 11 is pressed against the second electrode 12 at a pressure more than a specified pressure P.sub.0 (P.sub.0 =2 Pa, for example), as shown in FIG. 9B, the resistance is lowered to a few .OMEGA. or less. FIG. 10 illustrates this electrical characteristic of the pressure sensor 6.
FIGS. 8A and 8B show a properly loaded state and a misloaded state of the IV tube 1, respectively. When the IV tube 1 is properly loaded to be located on the fluid propelling portion 2, as shown in FIG. 8A, closing of the door 5 will not cause a pressure to be applied to the pressure sensors 6. Therefore, the resulting resistance value will be more than a few tens M.OMEGA.. On the other hand, when the IV tube 1 is misloaded so as to be displaced away from the fluid propelling portion 2 onto the pressure sensor 6 on one side thereof, as shown in FIG. 8B, closing of the door 5 will cause the door 5 to press the IV tube 1 such that a pressure higher than the specified pressure P.sub.0 will be applied to the pressure sensor 6. The resulting resistance value will be a few .OMEGA. or less.
Accordingly, it can be detected whether or not the IV tube 1 is properly loaded, by measuring the resistances of the pressure sensors 6. Moreover, when an misloaded IV tube 1 is detected, operation of the fluid propelling portion 2 is prohibited so that no danger will arise to the patient.
However, with the conventional pressure sensors 6 as described above, the resistance value will read more than a few tens M.OMEGA. in either case where no force is encountered and the pressure-sensitive conductive layer 11 is apart from the second electrode 12, as in FIG. 9A, or where the pressure sensors 6 have been thrown into an inoperative state such as a damaged or unpowered state. This makes it impossible to differentiate between the properly loaded state of the IV tube 1 and the inoperative state of the pressure sensor 6. The result is that even if the IV tube 1 is misloaded, the inoperative state of the pressure sensors 6 would lead to a misdecision as proper loading, which would be of great danger to the patient.